The present invention generally relates to a braking device, and more particularly, to a variable ratio of force-enlargement master cylinder for a braking device of a bicycle.
It is well known that a braking force generated from a friction pad of a rim brake system is used to halt a bicycle by clipping both wheel edges of the bicycle. However, the dust and moisture are easily accumulated on the surfaces of the wheel edges. Such a situation particularly occurs when the bicycle is ridden in a roadway covered with the mud or water. Therefore, operating circumstances of the friction pad go from bad to worse, resulting in many problems such as a brake performance reduction, or even the safety issues. Moreover, the cable is applied to transfer the braking force to the brake device at the wheel side. Since the cable will tend to be extended when the applied tension is too large when the braking lever is extremely pressed, the braking device will not give enough braking force in this situation.
To solve the above problems, a disc brake system 100 has been developed, as shown in FIG. 1. Braking fluid and the pipelines are used as the medium of transmitting the brake force to the braking devices. When the rider pulls the lever of the braking device with a force 102, the piston 104 in the braking device pushes the braking fluid through a guide tube 106. The braking fluid is pressed into a brake member 108 of the braking device to pull out the friction pad 112 to impel a piston 110 against a disc 114 of the brake member 108. The braking fluid, the single piston 104 and the piston 110 serve as transmission interface of the braking force in the disc brake system 100. A ratio of force-enlargement is defined as magnifying rate of a force between the single piston 104 and the piston 110. There is a need to increase the ratio of force-enlargement master cylinder.
If the cross-sectional area of the piston 104 and the piston 110 is reduced, the ratio of the force-enlargement is increased, which results in a reduction of braking force applied on the rider""s hand. However, such a situation of cross-sectional area decrement of the piston 104 diminishes the flow rate of braking fluid in the piston 104 and the displacement of the piston 110 is decreased and thus leaded into the following drawbacks: (a) The piston 110 has an insufficient forward displacement. Even if the piston 104 is entirely pushed down, the piston 110 still cannot propel the friction pad 112 onto the brake disc 114, which leads to an inadequate force imposed on the braking system. (b) The piston 110 has an insufficient backward displacement. Even if the piston 104 is totally released, the piston 110 with the friction pad 112 still cannot be separated from the brake disc 114, which leads to abrasion, vibration, noise and human power dispersion.
Consequently, how to control the brake speed and the braking force of the braking device and how to increase the braking force and the high ratio of force-enlargement are important problems and are currently main issues for braking device manufacturers of the bicycles.
The primary object of the present invention is that a friction pad of a variable ratio of force-enlargement master cylinder rapidly attaches to the disc of the brake member to increase the manipulation of the bicycle when a lever is dragged down in the beginning.
Another object of the present invention is that the friction pad of the variable ratio of force-enlargement master cylinder is imposed at a higher normal force to increase the braking effect of vehicles.
According to the above objects, the present invention sets forth a variable ratio of force-enlargement master cylinder. The variable ratio of force-enlargement master cylinder comprises a cylinder, an outer piston and an inner piston. The cylinder comprises a first cavity which includes a first opening, second opening and third opening on the periphery of the first cavity. The first cavity is filled with fluid stored in a fluid supply device.
The first channel located inside a sidewall of the cylinder is connected to the second opening with the third opening. The fluid in the first cavity is transmitted into the brake member by the first channel of the cylinder to apply pressure to the friction pad serving as an imposition on the disc of the brake member.
The outer piston, hollow and cylindrical in shape, is coupled to the first cavity of the cylinder by a first resilient body to reciprocate along the first cavity. The outer piston has a second cavity and a second channel inside a sidewall. The second cavity is connected to the first cavity of cylinder via the second channel to fill the second cavity with the fluid. Moreover, the outer piston includes a fourth opening and a fifth opening on the surface region of the outer piston to drain the fluid outwardly. An annular recess is preferably positioned on a surface region adjacent to the fourth opening of the outer piston to drain the fluid passing through the annular recess via the first channel.
The inner piston coupled to the second cavity of the outer piston is allowed to reciprocate with a second resilient body between the outer piston and the inner piston along the second cavity. More significantly, the cross-section area of the inner piston is smaller than that of the outer piston along the axial center. When the rider applies force to the inner piston, the fluid stored in the first cavity of the cylinder is quickly exhausted at a higher speed to push the brake forward and then the friction pad is pressed onto the disc at a larger-than-normal force. In addition, the inner piston has a third channel therein to circulate the fluid around the variable ratio of force-enlargement master cylinder.
In the use of the variable ratio of force-enlargement master cylinder, if a lever of the braking device is pulled, the outer piston compresses the fluid within the first cavity of the cylinder. Both sides of the third channel are aligned with the second channel and the fourth opening of the outer piston, respectively. Also, the fifth opening is shielded with the sidewall of the cylinder so that the fluid passes sequentially through the first cavity, the second channel, the third channel and the fourth opening. Finally, the fluid exhausts from the first channel to transfer hydraulic pressure to the friction pad of the brake member.
The friction pad of the braking member is propelled by the fluid with a higher speed to serve as the step of xe2x80x9cfast approachingxe2x80x9d. Therefore, the friction pad rapidly contacts the disc to increase the manipulation of the bicycle.
If the rider continuously presses the lever, the outer piston propels the fluid within the first cavity until the bottom of the outer piston contacts the bottom of the first cavity. Also, the third opening of the cylinder aligns with the fifth opening of the outer piston. Meanwhile, the fluid in the second cavity of the outer piston flows through the fifth opening of the outer piston and the third opening of the cylinder. Afterward, the fluid later is drained away from the first channel of the cylinder.
In contrast with the step of fasting approaching, because the effective cross-area of the inner piston is smaller than that of the outer piston, the fluid within the second cavity moves at a lower speed and at a higher pressure. Consequently, a higher pressure is transmitted into the friction pad to increase the normal force applied to the disc, which is a step of xe2x80x9chigh pressurexe2x80x9d to increase the variable ratio of force-enlargement.
In summary, the variable ratio of force-enlargement master cylinder makes the friction pad rapidly attach to the disc to reduce the braking time. After the friction pad contacts the disc, the friction pad continuously presses the disc at a higher-than-normal force to increase the variable ratio of force-enlargement.